Pretty much any decent USB 2 or 3 drive should be OK. I use a 64Gb USB3 Flash Drive for occasional recording convenience as my main recorder is a separate Sony HDD RDR870. I've also used a 500Gb USB 2 drive while initially experimenting with the record feature.
The drive normally has to be registered for recording (done via the menu's) and then the drive is 'locked' to your TV because of copyright issues, meaning you can't give the drive to someone else to watch what you recorded.
Setting the drive up causes the TV to format and create a non PC type disk structure and file table meaning you can only reuse the drive on a normal PC again if you first delete all that the TV has done (using the PC's disk management console).
From another thread of mine:
The removed drive is not recognised when connected back to a Windows PC for reuse. You have to go into the 'Disk Management Console' where you will see the drive but it will be showing (or rather not showing) a valid file format such as NTFS or FAT32. You need to delete the volume and then recreate a new 'simple volume' picking either NTFS (recommended for a traditional drive) or FAT32 as the format type. So your drive is still 100% OK, it just needs reformatting back to something Windows (or OS) can recognise.
https://community.sony.co.uk/t5/android-tv/usb-recordings-are-jerky-when-played-back/td-p/2271707
